1. Field of the Invention
The invention relates to a control apparatus for automatically stopping or starting an internal combustion engine, such as a gasoline engine, a diesel engine, or the like, upon satisfaction of a predetermined condition. More particularly, the invention relates to a control apparatus for making a determination regarding a stop of an internal combustion engine, and a control method of the apparatus.
2. Description of the Related Art
An internal combustion engine installed in a vehicle is stopped not only due to an intentional stop operation, but also due to a fuel shortage, an excessive drop in engine rotation speed, etc. Lately, an internal combustion engine is also stopped by a generally termed eco-run control of stopping the engine at a stop of the vehicle for the purpose of improving fuel economy. A technology in which an engine is stopped by the eco-run control is described in Japanese Patent Application Laid-Open No. 11-324755. According to the technology described in this laid-open patent application, at the time of an automatic run of the engine caused upon satisfaction of a predetermined condition, the standby time prior to execution of the automatic engine stop is changed in length in accordance with the magnitude of the braking operation force occurring during the state in which the condition is satisfied.
If the engine is stopped due to an automatic stop based on a generally termed stop control, or due to other causes, various controls associated with the stop are usually performed. Furthermore, as described in the aforementioned patent application, in the eco-run control, the engine is restarted when the satisfaction of the condition discontinues. Therefore, the determination regarding a stop of the engine needs to be performed electrically or mechanically.
Many conventional internal combustion engines employ a sensor that outputs a pulse signal at every predetermined rotational angle of an output shaft, for example, a crankshaft or the like, as a device for detecting the engine rotation speed. In this kind of internal combustion engine, the use of the sensor makes it possible to determine whether the engine has stopped. That is, if the engine rotation speed decreases, the pulse signal interval or the pulse width becomes long, and the duration from the time point of input of the previous signal to the time point of input of the next signal (generally termed update time) becomes long. If the engine stops, the pulse signal is no longer updated. Therefore, an engine stop can be determined at a time point at which the elapsed time from the previous signal update reaches a predetermined length of time.
[Problems To be Solved]
As described above, the engine stops for various factors. The behavior of engine operation occurring until the engine rotation stops varies from one stop factor to another. For example, if the engine comes to a stall due to an abnormality or a trouble, the change in engine rotation speed is not monotonous, but the engine rotation speed changes in a generally termed oscillating manner in which the rotation speed repeats increases and decreases until the engine finally stops. In this case, even if the pulse signal update time increases with the decreasing engine rotation speed during the process from the start of decrease in rotation speed until a stop of the engine, it is impossible to immediately determine whether the increased update time is a result of a stop of the engine or is merely an increased update time preceding a stop.
Therefore, the time allowed before determining a stop of the engine is set long in order to ensure reliable determination of a stop of the engine regardless of the kind of stop factor. That is, determination of a stop of the engine is made if a predetermined stop determination time elapses without update of the pulse signal.
In the aforementioned eco-run control, the engine stop control is performed upon satisfaction of a predetermined stop condition. If after that, a vehicle start request is made, the satisfaction of the predetermined stop condition discontinues and the engine restart control is to be performed. In that case, the engine restart control is executed only after a stop of the engine is determined. Therefore, the restart of the engine delays if there is a delay in determination of a stop of the engine.
Therefore, according to the engine stop determination and the subsequent engine restart control in the conventional art, a long time is needed prior to actual restart of the engine if a start request is made immediately after the engine stop condition is met in the generally termed eco-run control. Hence, various drawbacks occur. For example, a response delay in the start control causes discomfort, or causes laggardness.